A. We first see the building in Episode 10, of the final Season 8, "Goodbye Miami".

Oliver Saxon, the Brain Surgeon Killer, uses this former mental asylum as his lair and kill room.

When he was just 14, Saxon (AKA Daniel Vogel) killed his brother.

Realizing he was a psychopath, his mother, Dr. Elizabeth Vogel, had him institutionalized him at a similar asylum.

A few years later, he set fire to the asylum, killing several patients, and then assumed the false identity of Oliver Saxon.

We first see the place when Saxon takes his mother (Dr. Vogel) here, and shows her his kill room, with a restraint chair.

He tells
her it he has made it look just like the "treatment room" at his
childhood asylum, where they would strap him down and force-fed him
meds.

When she offers to put him in a better facility, he tells her that he
wants her to do for him what she did for Dexter: to teach him how to
survive free in the world as a killer.

At first,
she tells him that she can't help him kill innocent people. But
them feeling menaced by the lunatic, she tells him she will do whatever
is necessary to help him.

In the next episode (11, "Monkey in a Box"), this is where Dexter ties up Saxon and decides not to kill him. It's where Marshal Clayton accidentally lets Saxon go, and is killed as a result. And it's where Debra is shot in the final second of the episode.

Q. What is it actually in real life?

A. The old Hollywood Studio Club building.

Q. Where can I find it in real life?

This is 1215 Lodi Place, in Hollywood, between Fountain & Lexington.

The distinctive building has a very
colorful Hollywood history, dating back to the Roaring '20s and the
early days of Tinseltown.

It is the former YWCA Hollywood Studio Club,
a 1926 local
historical landmark which once offered low-cost lodgings to aspiring
young actresses, including Marilyn Monroe, Donna Reed, Kim Novak, Rita
Moreno, Ayn Rand and Barbara Eden.

It was, in effect, a chaperoned dormitory for young women trying to make
it in Hollywood, offering low rents and a safe environment.

A. In the early seasons, I
usually had to hunt down the locations after viewing the episodes, using
clues from the various scenes. By the now, though, I've developed
a small group of fans, spies & tipsters who kept an
eye out for Dexter filming in their neighborhoods, and let me know in advance when something is about to film there.

Between those reports, my own personal reconnaissance around town, and a
few new resources I discovered, by the time the new first episode airs, I
already know most (but not all) of the filming locations, and only
need to watch the episodes and match up the scenes with the correct
locations.